A number of regulatory reactions such as chromatolysis after axon injury, retrograde transneuronal changes, acute glial reactions and growth regulation according to the size of the peripheral field imply the existence of intracellular communicaton from the axons and/or terminals to the parent cell nucleus. Retrograde axonal transport may provide the means for this communication. We propose to study the retrograde intra-axonal transport of exogenous proteins such as horseradish peroxidase from the region of the axon terminal to the neuronal cell body in the chick visual system. We shall analyze by light and electron microscopy and biochemical techniques 1) the cytological organelles involved in transport, 2) the development of the transport phenomenon in embryonic chicks, 3) the effects of injury or alteration in the physiological state of the neuron on the retrograde transport of proteins, and 4) the possibility of applying additional markers to the further refinement of the retrograde technique as a tool for studying neuronal connectivity. BIBLIOGRAPHIC REFERENCES: Divac, I., LaVail, J.H., Rakic, P., Winston, K.R. 1977 Heterogeneous afferents to the inferior parietal lobule of the rhesus monkey as revealed by the retrograde transport method. Brain Res. 123: 197-207. LaVail , J.H., Nixon, R.A. and Sidman, R.L. 1977 Genetic control of retinal ganglion cell projections. Anat. Rec. 187: 634-635.